1. Field of the Invention
The present invention pertains to a permanent whipstock and placement method in a cased well for use in guiding a casing milling tool and the like.
2. Background
Producing oil and gas from subterranean formations through wellbores sometimes requires inspection of formation conditions to analyze production characteristics and prescribe future production techniques. Analysis of formation characteristics or changes is often dependent on the ability to take suitable core samples of the formation in the vicinity of the wellbore. Conventional coring operations require that the well be shut in while a drilling rig is brought in and operated to perform the coring operation. This process is time consuming and expensive and usually requires shut-in of the well and other procedures to reduce or eliminate fluid pressures at the surface during all phases of the drilling and core sample acquisition process.
Moreover, limitations on minimum core diameter and the inability to provide and set a suitable whipstock so that the casing can be milled out to gain access to the formation have, heretofore, precluded obtaining core samples through small diameter tubing strings and other wellbore structures of a diameter less than conventional casing diameters.
An improved method for minimizing the invasion of fluids into a core is described in a U.S. patent application Ser. No. 07/752,308 entitled: Method for Obtaining Cores From a Producing Well by Eric W. Skaalure, and a unique method for obtaining cores is described in a U.S. patent application Ser. No. 07/752,704 entitled: Coring With Tubing Run Tools From a Producing Well by Curtis G. Blount, et al., both assigned to the assignee of the present invention and both of even filing date with this application. The present invention provides a unique whipstock and placement method which is particularly advantageous for use in conjunction with operations for obtaining core samples from and through a well.